1. Field of the Invention
This invention relates generally to telecommunication systems, and, more particularly, to wireless telecommunication systems.
2. Description of the Related Art
The coverage area of a wireless communication system is typically divided into a number of cells, which may be grouped into one or more networks. Mobile units located in each cell may access the wireless communications system by establishing a wireless communication link, often referred to as an air interface, with a base station associated with the cell. The mobile units may include devices such as mobile telephones, personal data assistants, Global Positioning System devices, desktop or laptop computers, and the like. For example, a mobile telephone may initiate communication with a base station by providing a signal on an access channel. The base station may then use the received access channel signal to establish the wireless communication link between the mobile unit and the base station on a separate traffic channel. The mobile unit and the base station may then exchange messages over the air interface using the traffic channel.
At any given time, each base station may be expected to maintain concurrent wireless communication links with numerous mobile units. To reduce interference between the concurrent wireless communication links, the base station and the mobile units in the wireless communication system modulate signals transmitted on the assigned traffic channels using a predetermined code that uniquely identifies the mobile unit. For example, in a wireless communication system operating according to the CDMA 2000 standard, a public long code mask may be used to differentiate reverse link transmissions, i.e. from the mobile unit to the base station, over different traffic channels. The public long code mask is typically a 42-bit-long mask including two bits that indicate the type of long code mask (e.g. public or private), an additional eight bits that provide signaling information such as the method used to form the long code mask, and a 32-bit electronic serial number (often referred to using the acronym ESN) assigned to the mobile unit.
The proliferation of various types of mobile units has begun to exhaust the supply of 32-bit electronic serial numbers. To accommodate the growing number of mobile units, many practitioners have proposed replacing the 32-bit electronic serial number with a 56-bit mobile equipment identifier (often referred to using the acronym MEID: Mobile Equipment IDentifier). Under this proposal, a 56-bit mobile equipment identifier will be assigned to each mobile unit. For example, a unique 56-bit mobile equipment identifier may be incorporated into the hardware and/or software of each mobile unit. The 56-bit mobile equipment identifier, or another unique bit sequence formed based on the 56-bit mobile equipment identifier, may then be used by base stations to uniquely identify each mobile unit.
However, as use of the 56-bit mobile equipment identifier is phased in over time, many legacy systems may continue to use the public long code masks generated using the 32-bit electronic serial number. For example, a legacy base station may generate a public long code mask using the 32-bit electronic serial number. Accordingly, protocols that incorporate the 56-bit mobile equipment identifier typically provide for a pseudo-electronic serial number (sometimes referred to as a pseudo-ESN). For example, mobile units that operate according to the IS-2000 Revision-D standard protocol are able to form a 32-bit pseudo-ESN using a hashing algorithm to generate a 24-bit number and then combining this number with a leading 8-bit fixed pattern 10000000, which is sometimes referred to as a manufacture code. The pseudo-ESN can be used by a base station to distinguish Revision-D mobile units from pre-Revision-D mobile units using the 8-bit fixed pattern.
A pseudo-ESN may also be used to generate a public long code mask that may be used to identify the mobile unit to a legacy base station. For example, the pseudo-ESN may be used to generate a public long code mask that may be used to identify the mobile unit to a network that operates according to IS-2000 protocol revisions having a protocol revision number less than 11. However, the pseudo-ESNs, as well as the public long code masks generated using the pseudo-ESNs, may not uniquely identify each mobile unit to the base station. An air interface collision may therefore occur when two mobile units in the same sector (or in neighboring sectors) attempt to communicate with a base station on different traffic channels within the same carrier using the same public long code mask generated from a pseudo-ESN.
Air interface collisions may increase the frame error rate (or bit error rate) on the reverse link. The increased frame error rate may also cause the power control system in the base station to raise the transmission powers used in the mobile in an attempt to decrease the frame error rate. Since the frame error rate is caused, at least in part, by the air interface collision, raising the transmission power of the mobile units may exacerbate the effects of the air interface collision and increase the frame error rate. Thus, attempting to address the errors caused by the air interface collision by raising the transmission power may lead to a feedback loop that forces the mobile units and/or base stations to transmit at their maximum transmission power. Increasing the transmission power, potentially to the maximum transmission power available to the mobile units and/or base stations, in this manner may decrease overall system capacity.
Air interface collisions may also create crosstalk on the reverse link, particularly if the signal transmitted on the traffic channel by one of the mobile stations is much stronger than the signal transmitted by the other mobile station. Crosstalk may also result in a real or perceived reduction in call privacy. In some cases, air interface collisions may also result in dropped calls, a decrease in user-perceived quality of service, and other undesirable effects.
The present invention is directed to addressing the effects of one or more of the problems set forth above.